Picea sitchensis (Bongard
by Liz Heidbreder
Other common names: yellow spruce, coast spruce, tideland spruce
Sitka spruce is a long-lived conifer that may reach ages of 400-700
years (Alfaro and Omule, 1990). It was named after Sitka Island
off the coast of Alaska. The island is now called Baronof Island.
It is the largest spruce in North America and has been known to
reach heights of 70 meters and span 2 meters across. The largest
Sitka spruce known obtained a height of 93 meters and a span of
5 meters across (Taylor 1990). It is most often associated with
western hemlock. This spruce has been introduced and is now grown
widely throughout England, Ireland, Scotland, France and other
northern European countries. Sitka spruce can easily be identified
from other spruces and similar species particularly by its needles.
The needles are contrastingly flat, stiff and sharp. Each needle
comes from a square, raised, woody peg that remains on the branch
after the needle drops. Its cones hang downward from the branches
and have thin scales with jagged edges. Its bark is thin and scaly
with colors ranging from brown to purplish grey (Preston, 1987;
Harlow et al. 1991).
The native range of Sitka spruce begins at about the 39 o
N latitude in northern California and continues up the Pacific
Coast through British Columbia to the 61o N latitude
in south-central Alaska. Sitka spruce grows on the islands associated
with this area as well. It is usually found within a few miles
of the coast, but its widest distribution spans 130 miles. This
occurs on the mainland adjacent to and including the Alexander
Archipelago in Alaska and the Queen Charlotte Islands of British
Columbia. Restriction generally occurs with steep seaside slopes,
but it is most common in valley bottoms, coastal plains, and several
miles inland along larger rivers and streams. Sitka spruce is
found from sea level to elevations of 910 meters (3000 ft), but
usually below 700 meters ( 2300 ft ) (Harris, 1990).
The climate found in the range of Sitka spruce varies from the
more northern limits of the range to the southern limits. It is
compositely a climate with year-round abundant moisture, cool
summers and mild winters. Generally summer precipitation and snowfall
are greater towards the north. Towards the southern range fog
and moist oceanic air are very important for adequate moisture
needed for growth. In this region most precipitation is in the
form of rain during the winter. Annual precipitation is influenced
largely by local topography. Table 1 shows annual precipitation
rates for four locations in two states within the range. Temperatures
in the summer decrease further north in the range as do the number
of frost-free days. As with precipitation local variations do
occur. In some areas Sitka spruce is restricted to low elevations
near sea level where moist oceanic air and fog supply necessary
moisture during the summer months (Harris, 1990).
Table 1. Precipitation (ppt) in the Sitka spruce range.
|City, STATE||Ppt. (inches)||Ppt. (mm)|
|Little Port Walter, AK|
(Adapted from Harris, 1990)
The soils found in the range of Sitka spruce come from various
parent materials. They are classified as Inceptisols, Entisols,
Spodosols, and Histosols. Sitka spruce grows best on soils that
are deep, well aerated, moist and whose parent materials were
high in calcium and magnesium. It does not grow well on swampy
sites. It is commonly found on alluvial soils, sandy and coarse-textured
soils, and soils with a thick organic layer. Sitka spruce is an
early pioneer species on the young Inceptisols and Entisols associated
with glacial retreat and uplift from the sea. The soils are acidic
with pH ranges from 4.0 to 5.7 (Harris, 1990).
REPRODUCTION AND GROWTH
Flowering and Fruiting
Sitka spruce begins to produce cones around 20 to 40 years of
age. The female strobili or seed cones have wavy, papery scales
with ragged edges. They are usually reddish to yellowish-brown
in color. They usually are found in the upper portion of the tree
at the ends of primary branches. The male strobili or pollen cones
are red in color. They are found lower in the tree at the ends
of secondary branches. Male and female strobili can be produced
on the same branch. Early in the summer of the year before pollination
and the seeds ripening, reproductive buds are initiated. The cones
ripen the same year of pollination. Pollen is released in early
and late spring for the southern and northern portions of the
range, respectively. The onset of flowering is related to temperature.
Seed Production and Dissemination
Sitka spruce generally reaches sexual maturity between 20 and
40 years of age. This is when cones are first produced and their
prolific seed production begins (Cleary, 1978). Sitka spruce produces
seed every year, with mast production occurring about every 3
to 5 years (Harris, 1990; Harlow et al. 1991). This can be more
often in the southern part of its range and less often in the
northern part of its range (Harlow et al. 1991). The cones open
and release seeds during dry weather and close back up during
wet weather (Harris, 1990). The seeds, considered to be small,
are approximately 1/8 inch long with a 1/2 inch long wing (Preston,
1989). They may contain anywhere from 155,000 to 400,000 seeds
per pound (341,000 to 880,000 per kilogram), averaging 210,000
seeds per pound (462,000 per kilogram) (Harris, 1990; Lutz, 19963.).
Sitka spruce seeds are disseminated by wind at a distance from
one-half mile to 100 feet (Harris, 1990).
The basic Sitka spruce rotation in the United States spans from
90 to 120 years (Shaw, 1989). In many northern European countries
Sitka spruce is being widely planted with shorter rotations, ranging
from 30 to 60 years (Kula, 1991; Low, 1987).
Most of the provenance studies have been don in the European countries
that have imported Sitka spruce for reforestation and afforestation
timber production. Local variation in the climate make provenance
selection difficult. Studies have indicated that northern provenances
survive lower temperatures than southern provenances, while southern
provenances suffer more frost damage. There is a cline for decreased
vigor from Oregon to Alaskan provenances (MacDonald et al. 1957).
Southern provenances grew taller than Alaskan provenances (Lines
and Aldhous, 1957;Thulin, 1963) and the southern provenances also
had greater diameter growth (Jeffers, 1959). Specific gravity
was greater for the northern provenances (Jeffers, 1959). Canadian
provenances also showed a clinal increase in bark lignin compared
to more southern provenances (Wainhouse and Ashburner, 1996).
This is important in Sitka spruce's defense against insects and
Sitka spruce naturally hybridizes with white spruce (P. glauca)
when they occur together. They have also been artificially
hybridized. They have similar wood qualities and their hybrid
(P. lutzii) shows some resistance to the Sitka spruce weevil
(Pissodes strobi)(Gordon, 1984). Sitka spruce was also
hybridized with Engelman spruce (P. engelmanni) (Johnson,
1939). The frost hardiness of Engelmann spruce and the
fast growth of Sitka spruce was desired for further use in reforestation
outside the limited range of Sitka spruce. This was also the desire
for a cross with black spruce, but the hybridization was not as
The provenance studies primarily from European countries have
aided in Sitka spruce tree improvement. Progeny tests of 27 year
old improved stock predict a 15% gain in volume at the end of
its rotation over an unimproved provenance from Queen Charlotte
Islands (Lee and Rook, 1990). Sitka spruce would be considered
more widely for reforestation if the Sitka spruce weevil could
be controlled in the southern half of the range.
Sitka spruce can easily be raised from cuttings, but it is mostly
regenerated by seeds in the nursery (Low, 1987). Although Sitka
spruce was capable of reforesting itself rather quickly, demand
for quicker reforestation called for seedling production to speed
artificial regeneration practices. In Oregon, previously fallowed
seedbeds are fumigated with methyl bromide in September. The seedbeds
are prepared for sowing at the beginning or middle of May. The
seeds have been stratified for 30 to 60 days, soaked for 1 day,
drained, placed in cold storage in plastic bags for 30 to 60 days,
dried and coated with the fungicide captan. Then the seeds are
sown. The seedbeds are covered to protect against birds until
the seeds germinate 10 to 15 days later. Irrigation, fertilization
and fungicides are applied periodically during the growing seasons.
Roots are pruned vertically and laterally and thinned to the desirable
density at the beginning of the second growing season. Root wrenching
operations are performed several times. This stimulates both fine
root growth and diameter growth. Sitka spruce seedlings may spend
1 or 2 years in the seedbed before being transplanted (Eide, 1982).
During the 1970s bare-root production was being replaced largely
by container production of seedlings. Container production has
been more extensive in Canada than in the states.
Nursery pests generally consist of birds, mammals, insects, weeds and fungi. Birds will often eat sown seeds directly from the seedbed. This problem can be curtailed by covering seed beds until germination or by creating loud noises such as gun shots (Eide, 1982; Sutherland, 1984). Deer, rabbits and various rodents cause problems by browsing. Fencing can keep deer out of the seedbed area and rodents can be shot or poisoned with bait (Sutherland, 1984).
Insects pose another problem for nursery production. Aphids and springtails are partial to spruce seedlings. The use of the insecticide Diazinon is helpful in controlling both of these pests (Sutherland, 1984).
Weeds are also prevalent in nursery seedbeds. While hand weeding is practiced, herbicides are helpful and less expensive in ridding seedbeds of unwanted vegetative competition. Some common weeds found in Sitka spruce nurseries are various grasses, nutsedges, common purslane, lupines, clovers, vetches, nightshades dandelions and many more. Several herbicides are used in nursery production in the Pacific Northwest. These include, but are not limited to, Methyl bromide/chloropicrin fumigation, Oxyflourfen , Bifenox, mineral spirits, Napropamide, Paraquat, Diphenamid, Glyphosate, and Atrazine (Sutherland, 1984).
Several diseases and their causal agents are the target of nursery
managers. Damping-off, root rot and top blight are some of these
diseases. Damping-off is can be minimized with methyl bromide
soil fumigation and captan or benomyl seed treatments, drenches
or sprays. Root rot is commonly caused by the Fusarium fungus.
It too can be minimized by methyl bromide fumigation, as well
as, captan and benomyl drenches and sprays. Top blight is also
caused by the Fusarium fungus. Its treatments are the same
as mentioned before (Sutherland, 1984).
According to the British Columbia Forestry Commission, seedling
prices for Sitka spruce range from $150 to $613 per thousand,
depending on the grades (McDonald, personal communication, 1997).The
Industrial Forest Association in Washington quoted $ 265 to $275
per thousand for plug-one Sitka spruce seedlings (Crawford, personal
Sitka spruce regeneration in the wild often occurs in gaps created by fires and blowdowns. Bare soil is best for reforestation or afforestation (Alfaro and Omule, 1990).
Before reforestation, clearcutting is preferred. Sitka spruce
grow better in the open than in partial cuts like shelterwoods.
The area should be cleared of debris and vegetative competition
(Cleary, 1978). Furrrow plowing and site drainage are practiced
in Scotland before planting (Low, 1897).
Sites can be reforested or afforested by seeding or by planting
seedlings. Seeding is generally less efficient, but can be used
on sites that have limited access, rocky soils, and steep slopes(Cleary,
1978). Seedlings have a bout three years headstart over seeds.
New germinants and seedlings are more susceptible to environmental
stresses in their first year. Shovels and dibble bars are used
for planting on the west coast ( Blake and South, 1991). Mechanical
planting is uncommon (Cleary, 1978).
Insects and Diseases
There are several insects that plague Sitka spruce stands. The Sitka spruce weevil (Pissodes strobi) is a problem in Oregon, Washington and southern British Columbia (Alfaro and Omule, 1990; Mitchell et al. 1990; Harris, 1990). Due to the cooler summers in Alaska and northern British Columbia, the weevil cannot develop. The spruce aphid (Elatobium abietinum ) and the spruce beetle (Dendroctonus rufipennis) are a pest from throughout the range of Sitka spruce. Seedlings are the host of a root-collar weevil (Steremnius carinatus ) that girdles the stem (Harris, 1990). Insects should be controlled with insecticides at the time of planting.
Root rot in young Sitka spruce stands is caused by Heterobasidium annosum and Armillaria mellea. Butt-rot is caused by the fungus Fomes annosus (Harris, 1990).
Butt-rot can be minimized by treating freshly cut stumps with
urea (McCarthy and Keogh, 1983). Rosellinia needle blight (Rosellinia
herpotrichoides)also occurs in Sitka spruce nurseries. There
are no fungicides registered for this. The best control measure
is to decrease the seedbed densities to increase aeration and
decrease humidity (Cordell, 1989).
Sitka spruce is tolerant of shade. It can grow rather well in
competition with weeds if moisture and nutrients are not limiting.
Weed control is often practiced to enhance the already slow early,
growth rate. ( Austin and Abrahamson, 1984 ).
The specific gravity of Sitka spruce grown in the United States
is 0.37 and 0.40 for green and dry wood, respectively. Sitka spruce
from Canada has a specific gravity of 0.35 for green wood (Haygreen
and Bower, 1989 ).
Modulus of Elasticity (MOE)
The MOE of Sitka spruce grown in the United States is 1.23 and
1.57 million pounds per square inch (psi) for green and dry wood,
respectively. Sitka spruce from Canada has a MOE of 1.37 and 1.63
million psi for green and dry wood, respectively (Haygreen and
Bower, 1989 ).
Modulus of Rupture (MOR)
The MOR of Sitka spruce grown in the United States is 5,700 and
10,200 psi for green and dry wood, respectively. Sitka spruce
from Canada has a MOR of 5,400 and 10,100 psi for green and dry
wood, respectively (Haygreen and Bower, 1989 ).
Sitka spruce wood is light, soft, strong and flexible. Its high
strength to weight ratio lends it value for many uses. It has
been used for ship and airplane construction (Harris, 1990). It
is used for pulp and paper, panel board, fiberboard, particleboard,
veneer, saw timber, doors, oars, and turbine blades for wind energy
conservation systems(Cahalan, 1987; Thompson and Rook, 1990; Harris,
1990). Its high resonant quality is an excellent property for
use in making violins, cellos, guitars, sound boards for pianos
and organs (Harris, 1990).